1. Field of the Invention
The present invention relates to a recording apparatus including a recording head configured to perform scanning to form an image on a recording medium, and a method for controlling the recording apparatus.
2. Description of the Related Art
Recent inkjet recording apparatuses are required to perform high-speed recording on a recording medium. To realize high-speed recording, it is effective to reduce a number of passes in multi-pass recording that can realize high-quality recording. The “number of passes” represents times of scanning performed by a recording head to complete recording of a recording region corresponding to one band.
The multi-pass recording includes scanning a recording head and feeding a paper (recording medium), which are repetitively performed. The number of discharge ports provided on the recording head is constant. Therefore, reducing the number of passes can increase a paper feeding amount per feeding operation. For example, if a recording apparatus performs one-pass recording, the paper feeding amount per feeding operation is doubled compared to two-pass recording. As a result, recording speed of the recording apparatus can be doubled.
More specifically, if the number of passes decreases, the times of scanning performed by the recording head to complete recording of a predetermined recording region decrease. When the paper feeding amount per feeding operation increases, time required for completing the recording of the predetermined recording region becomes shorter.
A general inkjet recording apparatus is equipped with a recording head including a plurality of discharge ports capable of discharging ink droplets which performs scanning in a direction perpendicular to an alignment direction of the discharge ports to perform recording. Therefore, if the inkjet recording apparatus performs one-pass recording, the inkjet recording apparatus can complete recording of a band-like recording region corresponding to one band during one recording/scanning operation.
In this manner, when a recording apparatus performs one-pass recording, the recording apparatus completes recording of a recording region corresponding to one band during only one recording/scanning operation. An amount of ink discharged to a recording medium per recording/scanning operation is greater than that required for multi-pass recording that performs recording/scanning two times or more to complete recording of the recording region corresponding to one band. Therefore, when the recording apparatus performs one-pass recording, a portion having a higher image density than other portions (a black streak) may appear in a boundary portion between two recording regions formed in consecutive recording/scanning operations, if the recording regions have higher ink densities, although the degree of the black streak is variable depending on the type of the recording medium or ink(s).
Generation of a black streak tends to appear in a recording operation by an inkjet recording apparatus equipped with a plurality of recording heads each of which discharges different ink (yellow (Y), magenta (M), cyan (C), etc.) arrayed in a scanning direction thereof. The black streak can be referred to as “boundary streak.” Generation of boundary streak (s) may decrease recording quality to below an acceptable level.
As discussed in Japanese Patent Application Laid-Open No. 2002-96460, there is a conventional one-pass recording method capable of recording a high-quality image while reducing boundary streaks. The method includes determining values of hue and chroma in a target region of a boundary portion between consecutive bands based on ink discharge amounts. The method further includes setting a thinning rank for each ink and a recording position based on the determined values of hue and chroma, and performing recording while thinning out some data based on the thinning rank. As a result, boundary streaks appearing between consecutive bands can be reduced when a recording apparatus performs one-pass recording.
The above-described method for reducing boundary streaks basically includes inputting binary data (e.g., bitmap data) of Y, M, and C, or multi-valued data of red (R), green (G), and blue (B), from a host apparatus. If the input data is bitmap data of Y, M, and C, the method includes counting ink dots discharged for respective colors, setting a thinning rank for each color considering magnitude correlation of counted values of respective colors, and performing thinning processing with a mask pattern corresponding to the set rank.
If the input data is multi-valued data of R, G, and B, the method includes multiplying the input data by reducing coefficients (table values) to perform thinning processing in the process of converting the input data into corresponding Y, M, and C data. However, from the viewpoint of saving the memory capacity of the recording apparatus or reducing the number of gates provided in an application specific integrated circuit (ASIC), it is desirable that the data received from the host apparatus is density data of respective colors corresponding to ink colors in an image region with a predetermined size. Reasons for that are as follows.
To save the memory capacity, compression of data is effective. The above-described density data of each color is compressed data. A recording buffer can store a greater amount of information if the data is compressed. The amount of information usable for a calculation can be increased. Compression of data is a key to realization of high-quality recording and high-speed recording.
To reduce the number of gates of a central processing unit (CPU), it is desired that the input data received from the host apparatus can be easily converted into recordable data for a recording head with minimum processing. To this end, it is ideal that the host apparatus performs color conversion from R, G, B to Y, M, C or other processing placing a heavy load on the CPU, while the recording apparatus performs only processing that contributes to the high-quality recording and the high-speed recording. The processing contributing to the high-quality recording and the high-speed recording is, for example, processing necessary for executing multi-pass recording or image processing applied to the boundary portion between consecutive bands. Therefore, to perform this processing, the recording buffer should store recorded data corresponding to at least one band.
For the above-described reasons, it is desired that the data received from the host apparatus is desirably the density data of respective colors corresponding to ink colors in the image region with the predetermined size. However, the above-described conventional inkjet recording apparatus can process only bitmap data and multi-valued R, G, B data, and can not process density data of respective colors.
Further, according to the above-described conventional techniques, thinning processing applied to bitmap data (binary data) and color conversion from R, G, B to Y, M, C require different color gamut determination algorithms. Furthermore, the boundary portion between consecutive bands cannot be directly detected from R, G, and B data. It is therefore necessary to additionally input information relating to the boundary portion between consecutive bands from the host apparatus.